繫緊的鞋帶為什麼會鬆英語美文

You’re strolling down the street or maybe hauling that load of laundry down a flight of stairs when all of a sudden. Your laces come undone. If you’ve ever pondered what precipitates this pedestrian wardrobe malfunction, you might want to tie your shoes and beat a path to the Proceedings of the Royal Society A.

有一天你在街上漫步，或是搬著一大堆衣服下樓，這時突然……你的鞋帶鬆了。如果你也曾好奇過這種“行人服裝故障”的原因，那你可以繫好鞋帶，然後在英國《皇家學會會刊.A輯》中尋找答案。

In that journal, researchers have trotted out data that show that a combination of whipping and stomping forces is what causes laces to unravel without warning.

在該期刊中，研究人員提出的資料顯示，甩動和跺腳這兩種力的結合是導致鞋帶突然鬆開的原因。

The investigators noted that shoelace knots frequently fail when people are walking. But not when they are, say, sitting on the edge of a table and swinging their legs. Laces also stay tight when marching in place with no forward motion.

研究人員注意到，鞋帶結經常在人們走路時散開。但是當人們坐在桌邊晃腿時，鞋帶卻不會鬆。同樣，當人們原地踏步，不向前運動時，鞋帶也不會鬆開。

That led the gumshoes to suspect that stepping and swinging somehow work together to foil footwear security. But how? To untangle this knotty problem, the researchers made a slo-mo video of a student running on a treadmill, thus recording the literal steps that lead to catastrophic knot failure.

這使研究人員懷疑，踏步和擺動以某種方式結合會破壞鞋帶的穩定性。但這是怎麼做到的?為了解開這個難題，研究人員製作了一個學生在跑步機上跑步的`慢動作視訊，來記錄導致鞋帶鬆開的步數。

Here’s what they slowly saw: When the foot strikes the ground, the force of that impact causes the knot at the center of the lace to deform and stretch. And when the foot swings forward, the ends of the shoelace fly forward. That whipping motion pulls the knot open a bit more, which allows the free end of the lace to slip through a tiny bit. With each cycle of impact and whip, the free end slides a little more, until enough of it has come through that the knot finally unravels.

這是他們逐漸發現的現象：當腳著地的時候，這種衝擊力會導致鞋帶中間的結變形和拉伸。當腳向前邁的時候，鞋帶末端會向前飛起。這種甩動的動作讓鞋帶結稍稍鬆動，進而導致鞋帶自由端向外滑動一點點。隨著“衝擊和甩動”的一次次迴圈，鞋帶自由端持續滑動，直到鞋帶滑出，鞋帶結最終鬆開。

The researchers confirmed that some knots are stronger than others. The granny knot that most of us use on our shoes is fairly weak and prone to failure, perhaps because the knot winds up twisted when pulled tight. A square knot, on the other hand, held up well in the treadmill test. To get that knot to buckle, the researchers had to attach weights to the free ends to aid in the tugging of those whipping tips.

研究人員證實，有些結會更結實。我們大多數人在繫鞋帶時常用的是“奶奶結”，這種結其實不太結實，很容易鬆開，可能是因為我們拉緊鞋帶時導致鞋帶結變形。另一方面，平結在跑步機測試中表現良好。為了讓鞋帶結繫牢，研究人員不得不增加鞋帶自由端的重量，幫助鞋帶頭找到牽引感。

The researchers did not determine whether different types of laces are more likely to produce ties that bind. So though this initial study has made great strides in our understanding of shoelace mechanics, we still have a long way to go before this research is all tied up.

研究人員還沒有確定哪種鞋帶打結更結實。雖然初步研究在幫助我們瞭解鞋帶機理上取得了巨大進展，但是，在研究全部完成之前，我們還有很長的路要走。